model_path should be ignored as the checkpoint path (#11157)

* model_path is refered as the path of the trainer, and should be ignored as the checkpoint path.

* Improved according to Sgugger's comment.

examples/text-classification/run_xnli.py

@@ -332,13 +332,15 @@ def main():
 
     # Training
     if training_args.do_train:
+        checkpoint = None
         if last_checkpoint is not None:
-            model_path = last_checkpoint
+            checkpoint = last_checkpoint
         elif os.path.isdir(model_args.model_name_or_path):
-            model_path = model_args.model_name_or_path
-        else:
-            model_path = None
-        train_result = trainer.train(model_path=model_path)
+            # Check the config from that potential checkpoint has the right number of labels before using it as a
+            # checkpoint.
+            if AutoConfig.from_pretrained(model_args.model_name_or_path).num_labels == num_labels:
+                checkpoint = model_args.model_name_or_path
+        train_result = trainer.train(resume_from_checkpoint=checkpoint)
         metrics = train_result.metrics
         max_train_samples = (
             data_args.max_train_samples if data_args.max_train_samples is not None else len(train_dataset)